Means for depositing films of metal on a series of plates or sheets



SPORING ET AL MEANS FOR DEPOSITING FILMS OF METAL July 18, 1950 P. A.

ON A SERIES OF PLATES OR SHEETS Filed Aug. 12, 1946 6 Sheets-Sheet l Afro/mas y.

July 18, 1950 P. A. SPORING ET AL 2,515,358

- MEANS FOR DEPOSITING FILMS OF METAL ON A SERIES OF PLATES OR SHEETS Filed Aug. 12, 1946 6 Sheets-Sheet 2 0 O N If: 0 0 g 1: LC: 0 o O O 0 o U q,

U Q u 21;? x Q 'U U U "Q \g' [I k B a 7'] F o E] r U a [I 1 g [I m N n 9 ll [1 g 3 .U U o g Q l1 5 k (0 U U t 5E s 4Q //VV/V70/?S m PfACY /l. spam/mug. awn/was PJOH/V-SO/V July 18, 1950 P. A. SPORING ET AL 2,515,358 I MEANS FOR DEPOSITING FILMS OF' METAL ON A SERIES OF PLATES 0R SHEETS 6 Sheets-Sheet 3 Filed Aug. 12, 1946 A TTOFAQE'X y 13, 1950 P. A. SPORING ET AL 2,515,358

MEANS FOR DEPOSITING FILMS OF METAL ON A SERIES OF PLATES OR SHEETS Filed Aug. 12, 1946 e Sheets-Sheet 4 July 18, 1950 P. A. SPORING ET AL 2,515,358

MEANS FOR DEPOSITING FILMS 0F METAL on A SERIES OF PLATES OR SHEETS Filed Aug. 12, 1946 6 Sheets-Sheet 5 y 1950 P A. SPORING El AL 2,515,353

MEANS FdR DEPOSITING FILMS 0F METAL I ON A SERIES OF PLATES 0R SHEETS Filed Aug. 12, 1946 6 Sheets-Sheet 6 ATWF/VEX Patented July 18, 1950 MEANS FOR DEPOSITING FILMS OF METAL ON A SERIES OF PLATES OR SHEETS Percy Archibald Sporing, Hampton Hill, and- Charles Piercy Johnson, Hanwell, England, as-

signors to The Telegraph Condenser Company Limited, North Acton, England, a British com- Application August 12, 1946, Serial No. 689,988 In Great Britain March 15, 1945 13 Claims. 1

The present invention relates to a method and means for depositing films of metal'on a series of plates or sheets and has been especially, although not necessarily exclusively, evolved for the purpose of depositing such a film on plates of mica intended to form the dielectric in electnical condensers. Heretofore it has been the practice todeposit such a film of metal either by a painting or spraying process, the material painted or sprayed, referred to in the following description and claims as paint, being either a compound of the metal, which, by subsequent treatment, is reduced to the pure metal or the metal itself directly deposited in fine particles. The process. is commonly referred to as silvering, but, in the following description and claims, that term is to be understood as covering the application of metals other than silver; also the term mica is to be regarded as including other materials in sheet form to which the invention is applicable.

The invention is concerned with forming a metal deposit on successive plates by a spraying operation, which possessescertain advantages over forming the deposit by painting. Very generally it is not desired to cover the whole of either side of the mica. or other plate to be silvered, but only a portion thereof, and for this purpose it has hitherto been the practice to spray the metal or metal compound onto the plate through a metal mask wherein there is cut an aperture determining the area on which the spraying operation is to take place. Obviously, a certain amount of the metal paint becomes sprayed on the marginal portion of the metal mask and it is necessary periodically to arrest the operation in order to clean this paint off; even if a duplicate mask be substituted while the mask which has been in use is cleaned, interruption in the continuous operation of spray painting is involved, and it is the main object of the present invention to overcome these and other dis-advantages arising from the use of a. metal mask.

According to the invention, in a spray painting operation as above set forth, a series, of masks is cut in paper Or other material of small value as compared with metal, each mas-k being disicarded at or before the stage at which paint has been deposited on the margin of the aperture cut therein to such an extent as would require a cleaning operation. It may be found desirable to use the paper masks once only, but, on the other hand, they may be employed two or more times as found convenient. In any, case, however, the paper or other material, referred to in the following description and claims comprehensively as paper, being relatively of small value, may be discarded when it has become useless owing to the encrustation of paint thereon. The apertures to form the masks might be cut in separate sheets of paper, but it is preferred to cut a series of apertures in a strip which may be wound off from a roll of paper and wound on to a second roll which is thus ready to provide a perforated strip constituting a series of masks. Preferably, however, the operation of cutting the apertures in a. strip and the use of such a strip in a spraying operation are combined in a single machine.

In order that the invention may be clearly understood and readily carred into effect, it will now be described more fully with reierence'to the accompanying drawings which illustrate, by way of example, a machine suitable for silvering small mica sheets and wherein:

Figures 1 and 2 together constitute a plan view of the machine,

Figures 3 and 4 similarly show a side elevation and Figures 5, 6, '7, 8 and 9 are respectively sections on the lines AA, 3-13, C'C, DD, and E-E, Figures 5, 6 and 8 being toan enlarged scale.

The machine is of the type wherein the apertures constituting the masks are cut as a series in a strip of paper. The various items constituting the apparatus are mounted on a bedplate or bench I, supported from which, by means of :uprights 2, is a roll of paper strip 3, the mounting being such that the strip may readily be drawn from the roll, but any suitable braking mechanism, not shown, since its construction does not form a feature of the present invention, is provided so that overrun of the paper is avoided. The strip 3 is lead over rollers '4, around a drum 5 and around a further roller 6: it then travels horizontally, being suitably supported and guided, and is finally taken underneath a roller l to a Winding-011 roll 8. The various operations of the machine are derived from a shaft 9 continuously rotated from a suitable source of power, not shown, by means of a belt l0, pulley II and worm gearing housed in a casing I2. By means of bevel gearing l3, the shaft 9 drives a spindle I4 on which the winding-off roll 8 is mounted, being driven therefrom through friction mechanism I5-so that continuous tension is maintained on the strip 3 between the rollers 6 and 8. For the purpose of the various operations of the machine it is necessary that the strip 3 shall be moved forward in a step-by-step manner, this being accomplished by means of a ratchet wheel l6 mounted on the spindle of the drum and actuated by a pawl IT. This ratchet-and-pawl mechanism is operated from the haft 9 by means of bevel gearing l8, serving continuously to drive a spindle I9, fitted with a disc 20 having a crank pin 2| which engages a connecting rod 22, the further end of which is pivoted to a lever 23 adapted to rock around thespindle of the drum 5 and carrying the pawl ll. Thus a rocking motion is imparted to the lever 23 and by the action of the pawl I1 the necessary step-by 'step movement is transmitted to the drum 5 and thence to the strip 3. 0h account of the frictional drive of the winding-off roll 8 the strip is maintained taut in its passage through the machine.

For the purpose of forming in the strip 3 a series of apertures to constitute masks through which the spraying opration is performed, it is passed through 'ajpun'chihg' device constituted'by punchin tool'Zl; Figure .5, carri'edby a mem- 'ber 25 adapted to be reciprocated relatively to @a dieZB. A plate Z Tis also supported by springs 28 "from the member 25, the punch z'a extending through the plate?! whenit operates to cut an aperture in the strip 3. Onwithdrawal of the punch, the plate 2'! remains in 'contactfwith the upper surface of thed'ie'QG sothatj the strip -3 is retained againstdthe upward motion of the punch 24 in order to avoidtearing the strip:

finally the plate 21 rises; liberating'thestrip 3 for its next step "forward. The memberfi and elements attached to it are reciprocatedperiodically by means of ajlever 29 with which the emb 25 e ec h aspira d in .9 Thelever Z9 is pivoted'at a fixed point 3|, its

rear end being provided with a roller bearing on a cam 33 carried by the shaft 9. A weight I 4 n the rear. nd.0fthe, ev s ves tpire the member 25 after passage of the cam 33 past theroller 32.

For the purpose of "siiteiingtne'im'ca plat -it is necessary to bring, each one separately, w ile the strip 3 is stationary, to a point immediately abovea spraygunr35, the location of thisspray gun vrelatively to thegipunch being such that at "each halt of the stripan aperture is immediately above the gun. In the machine illustrated, the

:latter is shown as fixed, but if the apertures in the strip 3 bejabo've a certain size,in order that the corresponding arearof each mica plate may be satisfactorily covered, it rnay 'befinecessar'y that the gun shall bemoved during the spraying operation. For thistpurpose -it may be pivotally column of mica plates contained in the magazine.

Into the bottom of l the magazine there opens a pipe 31 by means 'of which connection is'mad'e to an air-pressure "supply. The pressure thus exerted on the underside oi the piston is suffi- 'cient tosupport its weight and that of the mica plates and to ensure thatth'e'uppermostplate of the stack is in"'p"roxifnity to the upper open en of the magazine as; "If desired, thi's'open :endmaybe provided with a flange or pf'ojecti'o'ns directed inwardly'in order to preventthe plates being ejected from the magazine by the air pressure acting on its piston.

For the purpose of transferring the mica plates one by one from the magazine 36 to the op erative position of the spray gun 35, the suction picker illustrated more particularly in Figure 6 1 is employed. This picker comprises a nozzle 38 mounted on an arm 39 attached to a frame 40 which is free to reciprocate in the vertical direction "on rods 4|, the nozzle 38 being connected by a flexible tube '42 with a suction supply not shown, The rods 4| together with upper and lower members '43 and 44 constitute a framework supported above-and below between pivots and adapted tobe rocked in the horizontal direction through. a right angle. This rocking motion is 'd'erived'from a cam 46 mounted on the spindle l9 and adapted to act, against the pull of a spring 41, on a cam roller 48 carried by a lever 49 pivoted at50. Pivoted to the lever 49 is a connecting rod 5| "whichis 'al'st') jointed' t o an arm 52 on thefineihbr "44. Thus 'theno'zzle'38 "may be brought: ei'th' rinto a posh ion immediate- 1y abovethe meazmesscratote the spray 35.

For the "purpose or imparting the necessary t thelframe"40""alongther6iis dbn the shafts a' c'ain 5 of the shape show co-operate with roller-i541 carried by 55 pivoted to ahxeol at D55 ahd'fhaving a compression gp fig 57; ctirig n oppositioh L to and,bonnet?t'd- 1 a lll' by tr unnio ns a, .i t q t e r PS s e s, r th mec a sm represe teain Figure '6 is "that in which the nbz' z'l etfiisfi j m s i ma i e {ma zi on h right-hand lobe oi the cam '5 3, (as"viewed in Figure '6) operating on the-*rollerm he "nozz e Tnjthe the cam 53. The

"ri'o'zzle' is above" shown in Figui" nozzle 3fijiscontact with the strip 3.

While; the plate is thus held in Contact with the strip and over the aperture 'imifieamtay I is n'ecessary'that the latter'shall befactuat in tifderto perform the silvering o'pe ti n" neither 'sur cc of "the plate. :l or this purpdse',"the spraygcn"ss i 6nnected with a "'suitabl'e source*of "the "silverihg medium, suenjas ti -reserved, by bra pipe 59 and also ay je'li'fl withanair pressure uppl a I. "Thissupply '15 through the medium of a VaIVetZfFi'guieE, 3adapted to be openedwhena pintsextefidihg-rromrt is pressed home. This action is lft'd by means of-"a lever 64, pivoted 'at""'65 ahd adapt'dto *be acted upon by "an arm "66 fitted on the ea n- 1 provided With'a roller 61 wli-ich bafs' Oh the lever '64. Thllsf'oflfif in" eacnreyorution bf the shaft'9 and attheappropriate hent, thew/awe 63 is opened and' spr'ayfiisernitted froni'the gun 35, whereby the lower surfaced th'e lrfica pla te held by'the nozzle" nuit-contact With the Strip above the I 3 .is silverd. Ifdesired, the spray gun 35 may beeprovided with a shield which in normal operation of the apparatus is removed immediately before emission of the silvering medium provided that a mica plate is in position for silvering, such removal not, however, being effected if for any reason a plate is absent. The removing mechanism might, for instance, be actuated by a suction device connected With the tube 42; .if then there be no mica plate over the nozzle 38, the suction in this tube is destroyed or sufficiently reduced to ensure that the removal mechanism is not operated and the spray gun 35 remains shielded.

The mica plate having been silvered on its lower surface, it is necessary that it shall remain onthe strip 3, and for. this purpose the suction supply to the nozzle 38 mustbe cut off. To this end there is interposed in the tube 42 a valve comprising a cylinder 88 having a plunger 88a actuated, against the tension of a spring 89, by a cam "ID on the shaft 9. This valve is so constructed as to maintain suction over the greater part of each cycle of operations represented by one revolution of the shaft 9, but to open a port 682) in the cylinder 68 to atmosphere so as to break down the suction and produce atmospheric pressure at the nozzle 38 at the moment at which the silvering is completed and the nozzle is about to be raised in order to pick up the plate which has now become uppermost in the stack contained in the magazine 36. For this latter purpose the plunger 68a closes the port 68b to atmosphere, whereby the suction at the nozzle 38 is restored shortly after the latter has been raised from the mica plate deposited on the strip 3 and carried forward thereby. In order to raise the nozzle 38 from the strip 3, the left-hand lobe of the cam 53 (as viewed in Figure 6) comes into operation and maintains the frame 40 and nozzle 38 in the raised position during action of the cam 46, which allows the lever 49 to rock under pull of the spring 41 and turn the arm 39 counterclockwise (asseen in Figure 1) through a right angle, so that the nozzle 38 is once again above the magazine 36. The portion of the cam 53 between the lobes then becomes operative so that the nozzle 38 is lowered into contact with the uppermost mica plate on the stack and the cycle of operations is repeated.

. Meanwhile, the strip 3 is moved forward step by step carrying with it the series of mica plates, after each has been silvered on its lower surface. In its travel toward the winding-off roll 8 and immediately after the silvering operation, the strip3 bearing the mica plates may be passed through, or in proximity to, some heating element whereby preliminary drying of the silvering coating may be effected. Before the strip 3 reaches the winding-off roll 8 it becomesnecessary to remove the mica plates therefrom, and for this purpose the suction device illustrated in Figures 2, 4, and'8 is employed. i I

This mechanism serves to transfer the mica plates one by one from the strip 3 to an endless travelling belt II whereby the plates are conveyed through an oven I2 for heat treatment. It com prises a hollow arm I3 having a nozzle I4, this latter being shown in Figures 2 and 4 in the position. in whichit is about to pick up a mica plate a from the strip 3, and in Figure 8 immediately after it hasdeposited a plate on a platform in readiness for actual transfer 'to the belt II. The arm I3 is carried by a hollow spindle 15, mounted so as to be capable of rocking and fitted .with, a

pinion I6 engaging a segmental rack TI, pivoted at I8. In proximity to this mechanism there is fitted on the shaft 9 a cam I9 which bears, on a roller 88 carried by a lever 8| pivoted at 82 and connected with the segmental rack 'I'I by a link 83, the connection of the latter with thelever 8I being by means of a pivot .84, the location of which in a slot 85'may be variedin order to determine the degree of oscillation of the rack II and therefore of the hollow arm I3. The hollow pivot 15 of the arm I3 is connected by a tube 86 to the suction supply so that normally during the backand-forth stroke of the arm 13 there issuction at the nozzle I4. By this means when, during a halt in the motion of the strip 3, the nozzle 14 is brought down into contact with one of the mica plates and immediately subsequently is raised, the mica plate is carried with it through the travel of the arm amounting to nearly 180. However, as the arm I3 approaches the end of its backward stroke, the nozzle 14 passes between a pair of parallel plates 8'! the distancebetween which, while being sufficient to allow passage of the nozzle, is such as to retain the mica'plate, whereof the edges extend beyond the nozzle. In order to permit this deposit of the mica plate on the platform constituted by the plates 8i, it is arranged that a port in the hollow spindle I5, not shown, shall co-operate with a port leading to the atmosphere whereby the suction at the nozzle I4 is relieved. Further, the cam 19 is preferably so shaped that, as the nozzle I4 passes between the plates 81, its rate of motion is reduced so as to avoid any tendency for the mica plate deposited on the plates 81 to rebound. It will be observed that the silvered surface of each mica plate is now uppermost.

Mechanism for transferring the mica plates on to the endless belt ll then comes into operation, this mechanism comprising a bar 88 whereof the end is fashioned as a claw 89, adapted, when the bar 88 is reciprocated, to bear on the rear end of the mica plate resting on the plates ill and, on return movement of the bar, to slide the mica plate along the plates BI and finally to transfer it to the endless belt II. Reciprocatory movement of the bar 88 is effected by a cam 98 fitted on a spindle 9| driven from the shaft 9 by bevel gearing 92, this cam acting, against a tension spring 93, on a roller 94 mounted on a lever 95 pivoted at 96 and slotted at its upper end to engage-a pin 91. This pin is attached to a carriage 98 adapted to reciprocate along slide bars 99, the pin 91 extending through the carriage and serving as a pivot for the bar 88. In order that the claw 83 on the bar 88 shall not come into contact with the mica plate resting on the plates 81 during travel of the plate 88 from right to left as seen in Figures 2, 4 and 8, there is provided a ramp consisting of a short length of spring steel I00 whereof the left-hand end is raised, being attached to a block IllI, while the righthand end is sufficiently depressed to ensure that a pin I32 projecting from the bar 88 shall ride over the ramp. As, however, the bar 88 moves from right to left, after the pin I92 has travelled the length of the ramp I88, it drops over the raised end thereof, so that the claw 89 rests on the plates 81 and, on the return movement of the bar, serves to drag the mica plate along the plates 31 and transfer it on to the endless belt 'H, which is in continual movement toward the oven I2 and whereof the terminal roller I03 is convenient.- ly located in proximity to the bars 81. The mica plate having been removed from these bars, the

alumna 7 way is open'for return motion of the nozzle 14in order to pick up succeeding mica plate from the strip .3, the cam 19 being appropriately shaped in order to effect this retu n at the requir d moment andthe suction at the nozzle'being restored.

What we claim and desire to secureby Letters Patent of the United StateSis:

1. Apparatus for depositing films of metal on a Series f plates, comprising combination magazine wherein said plates are stacked'means for feeding a continuousstrip of paper-pastand in .close proximity to the magazine in the vdirece tion of the-length of the paper in a-step by step manner, a single, continuously operating drive unit'of substantial length extending lengthwise of the paper strip, and mechanism coupled with and operated by said unit-at each halt of said strip, including a punching tool for cutting an aperture insa-id strip, a pivoted arm, means for oscillating said arm between said magazine and a position on saidstrip over one of said apertures cutgduring a previous haltof said strip,means: for e cting the 'ni kin p f a p a e by the a m from th masa ine nd th depo i nsof the pl on h s p, a p a n p t 'z l l cated to spray paint through said aperture onto a plate tr nsferr d y sa d n a -ma z e to said strip, and 'means for removing from said strip one of said plates painted-during a halt of said strip.

'2. Apparatus as in claim 1, wherein the said means for picking up and depositing the plate comprises a suction nozzle-carried by the arm adapted to effect the transfer of he plates one by one to positions on said paper strip over said apertures.

3. Apparatus as in claim 1, wherein the said means ,for picking up and depositing the plates comprises a suction nozzle carried by the arm and connected to a source of suction, and said means for oscillating said arm comprising a coupling between the arm and said drive unit including a cam, a camactuated lever and a-con-necting-rod between the 'lever andthe arm, for automatically the apertures said paper strip and lowering thenozzle over said aperture.

4. Apparatus as in claim 1, whereinthe said means'for picking up and depositing the" plates comprises a suction nozzle carried by the arm, meansforming a coupling between the arm and the drive unit operating at each halt of said Strip for maintaining said nozzle during each transfer operation for an interval of time in priximity to said paper strip, said spray gun being located on the side of said strip. opposite to said nozzle, and means to operate said spray gun during said interval to silver the surface of one of said plates held for the time being bysaid nozzle.

5. Apparatus as in claim 1, wherein the said means for picking up and depositing. the. plates comprises a suction nozzle carried by the arm and connected to a source of suction, said means for oscillating the arm comprising a coupling between the arm and the unit operating at each halt of said strip for callsing'said nozzle 'to transfera plate from said magazine to said paper strip, said. spray gun being designed to function during 8 proximity-of said'nozzle to said papen'strip, means for relievingsuction pressure at said nozzle. upon completion of operation of th ;gun,.and meanS for restoring said nozzle to operative position relative to said magazine for taking-up another plate. a

6. Apparatus as in claim 1, wherein themechanism forrernovingthe platesfrom thepaper'strip comprises aepivotally mounted-suction nozzle and means for intermittently swinging the .nozzle to a positionto pickup aplate'from the strip.

7. Apparatus as inclaim 1, wherein the mecha nism for removing :the plates from the paper strip is constituted by a hollow arm "connected to a- 'source of suction, a suctionnozzleerr-said arm, a platform, and means forming-ac p ng between the nozzle and the drive un-itopera-ting automatically at each haltiof said strip for 1 001;.- ing said arm whereby saidplates are transferred one by one from-said paper. strip to'said platform.

Apparatusas' in claim .1, wher n the m chanism for removing the plates from-the paper st. is constitutedvby ahollow a-rrnconnectedp -r source of suction, a -suction nozzle onasaid arm, asplatform constituted :by a-pair of :plates, and m ns f rmi g a c upl ng be ween the n zzle and said drive unit operating automatically at each halt .of 'said strip for rocking said arm whereby said plates on said strip are transferred one by on m-said paper s ripte-s dpl t orm, said pairzof platform plates heingso located-that such nozzle, in its transferring movement, pfl l fis between'them,

i9ApparatuS=as in claim 1,- -inoluding. a plate form, the said means for moving the plates from the strip'comprising a -movable suction nozzle, means: for moving the suction; nozzle tin a prescribed path to -transfer said plates one b'y'one tfrom said. paper strip tosaid platiorm,==a roller, means for rotating said roller, anendless belt around said roll and means for tr ns: ferring'each of said p-lates from said platiorm to. said belt.

10. Apparatus as in claim 1, including. aplatform, thesaid means formovingthe platesfrom the strip comprisingramovable suction :inQZZlB, means for moving the suction nozzle ina'-. predescribed pathto transferrsaid plates one by one from said-paper strip to said platform, a roller; means for rotating saidi'roller, an endless-belt around said roller, a claw, means for oscillating said clawbetween said 1 platform and said: belt, and means for "holdingisaid claw out of contact with said platform during oscillation in one die rection, but allowing it to 'makecontactwith saidplatform during oscillationinthe reverse direction and thereby *to'bear on' the end of one of said plates resting on said platform whereby said plate is transferred to said endless belt.

ll. In'apparatus for depositing films of metal upon plates including an aperturedmaslringstrip moved intermittently in the direction of its length and spraying means located beneath the strip for discharge against the underside thereof; means for supporting a stack of plates adjacent to t-he strip, a plate transfer'mechanism adjacent to the plate stack supporting-'means and:functioning automatically to transfer-a plat from'th'e stack into' position over anopening on the: strip-bee tween the periods of movement offthe strip; heat treating-means for the sprayed platesicomprising a carrier belt disposed inispaced parallel relation with said strip, and means for transferringa' plate from the apertured strip to said belt Loom: prising 'a'su'ction nozzle,- supporting means :rfor

said suction nozzle for swinging the nozzle on an axis between and paralleling the strip and belt, said nozzle when in one position being in contact with the top of a plate on the apertured strip and when in another position being adjacent to said belt, means for swinging said nozzle from one position to the other, and means for effecting the removal of the plate from the nozzle and onto the belt when the nozzle is in the said other posi- 'tion.

12. In apparatus of the character stated in claim 11, the said last named means comprising a pair of spaced plates between which th nozzle passes for the removal of the nozzle carried plate, and reciprocating means overlying the said pair of plates for shifting the nozzle transferred plate onto said belt.

13. In apparatus of the character stated in claim 11, the said means for transferring the sprayed plate from the nozzle to the belt, com prising a pair of relatively long platform plates disposed in spaced parallel relation over and extending lengthwise of the belt at one end thereof, said nozzle being adapted to pass between the platform plates to leave the sprayed plate thereon, a claw member supported for movement longitudinally of and Over the platform plates, means for reciprocating said claw member, and means for moving the claw member over the top of the sprayed plate when the claw member moves in one direction and for lowering the claw member to engage the sprayed plate when the claw member moves in the opposite direction to effect the shifting of the sprayed plate from the platform plates onto the belt.

PERCY ARCHIBALD SPORING.

CHARLES PIERCY J OHNSON REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 954,751 Mann Apr. 12, 1910 1,822,769 Eitzen Sept. 8, 1931 1,855,749 McCarthy Apr. 26, 1932 1,988,065 Wooddell Jan. 15, 1935 1,999,903 Harshberger Apr. 30, 1935 2,134,041 Hamm Oct. 25, 1938 2,260,553 Boyd Oct. 28, 1941 2,294,273 Buxbaum Aug. 25, 1942 

